Ketonization of oxygenated compounds in pyrolytic products of biomass is an effective means for deoxygenation and upgrading of bio-oils. However, the ketonization potential of biomass-derived sugars and the mechanism underneath remain unclear. On this basis, a series of Fe doped CeO 2 catalysts were synthesized and employed for catalytic ketonization of xylan. Characterization of the catalysts proved the successful formation of the Fe-CeO x solid solution. Doping an appropriate amount of Fe (20–33%) ions on CeO 2 could obviously increase the number of oxygen vacancy and basic sites by up to 56.31% and 29.6%, respectively. During the catalytic reaction of xylan, pure CeO 2 exhibited a good ketonization ability during xylan pyrolysis, and the introduction of a certain amount of Fe further enhanced the ability. The highest yield of ketones was obtained by 33%Fe-CeO 2 , which was 38% higher than pure CeO 2 . The selectivity to linear ketones (acetone and 2-butanone) reached a maximum of 85% for 57%Fe-CeO x . Thus, oxygen-rich compounds had been converted to low oxygen containing and high-quality ketone components. Introducing Fe into CeO 2 favored the production of ethylene glycol rather than 2,3-dihydroxy propanal, and thus promoted the yield of acetone. This investigation provides fundamentals for the deoxygenation of biomass through catalytic ketonization, aiming at the production of value-added ketone products.
Amadori compounds, produced during Maillard reaction , are considered as precursors of flavor compounds . On the basis of Amadori compounds, herein two Amadori analogues, di- O -isopropylidene-2,3:4,5- β - D -fructopyranosyl alanine ester (A-ARP) and di- O -isopropylidene-2,3:4,5- β - D -fructopyranosyl proline ester (P-ARP), were chemically synthesized and their possibility as flavor precursors was evaluated by thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), and pyrolysis gas chromatography-mass spectrometry (Py-GC/MS). TG-DTG analyses indicated that the samples were stable at room temperature , and the largest mass-loss rates ( T p ) were at 208 and 278 °C, respectively. Upon thermal pyrolysis, the major flavor substances were butan-2-one, ethyl propionate , furfural , and dl -limonene for A-ARP, while 2,5-dimethylfuran, heptan-2-one, acetophenone , and 1 H -pyrrole for P-ARP. The flavor profiles are different from that of corresponding Amadori compounds, and are influenced by pyrolytic temperatures. These results provide one method to regulate the species and amounts of the degraded flavor products. Finally, the possible mechanisms of the pyrolytic processes are proposed.
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